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Three-DImensional Cosmic-Ray Simulations: Heliographic Latitude and Current-Sheet Tilt
Jokipii, J. R.; Kóta, J.
We present the results from a study of the variations of the cosmic-ray intensity with time, heliographic latitude, and longitude, and for varying interplanetary conditions, using our three-dimensional, time-dependent computer code for cosmic-ray transport in the heliosphere. Our code also produces a solar-wind and interplanetary magnetic field (I…
Non-LTE line formation for iron group elements. III. Fe IV.
Butler, K.; Becker, S. R.
A non-LTE line formation calculation for FeIV is introduced. The data for radiative bound-bound transitions which have been derived as part of this work are described and their accuracy is evaluated. The theoretical non-LTE spectrum of FeIV is compared to the HST spectrum of BD+75 325 and the IUE spectrum of Feige 67 both of which are classified a…
Cosmic Ray Modulation in the 3-D Heliosphere
Simpson, J. A.; McKibben, R. B.; Zhang, M. +2 more
The basic physical processes that lead to the long-term modulation of cosmic rays by the solar wind have been known for many years. However our knowledge of the structure of the heliosphere, which determines which processes are most important for the modulation, and of the variation of this structure with time and solar activity level is still inc…
The luminosity-dependent broad-line region in active galactic nuclei
Gondhalekar, P. M.; O'Brien, P. T.; Goad, M. R.
We investigate the effect of non-linear line response on the observed variability characteristics of the broad emission lines in AGN. The line response is intrinsically non-linear due to the dependence of the thermal and ionization structure of the line-emitting gas on the incident continuum flux. The BLR models we use include the effect of emissi…
Ultraviolet spectral evolution of star clusters in the IUE library.
Alloin, D.; Bonatto, C.; Bica, E.
The ultraviolet integrated spectra of star clusters and H II regions in the IUE library have been classified into groups based on their spectral appearance, as well as on age and metallicity information from other studies. We have coadded the spectra in these groups according to their S/N ratio, creating a library of template spectra for future ap…
A model for the circumstellar nebula of SN 1987A
O'Brien, T. J.; Kahn, F. D.; Lloyd, H. M.
Supernova 1987A in the Large Magellanic Cloud is surrounded by an extended region of nebulosity likely to be composed of material ejected during the evolution of the progenitor star, and which has been subsequently illuminated by the supernova event itself. Recent Hubble Space Telescope (HST) images have revealed the presence of two large elliptic…
Multiwavelength analysis of active galaxies: implications on unified Seyfert models.
Mas-Hesse, J. M.; Rodriguez-Pascual, P. M.; Wamsteker, W. +4 more
We have analyzed the multiwavelength (radio to X-rays) observational properties of a sample of 111 galaxies covering a wide range of activity (QSO, Seyfert 1 and 2 and star forming galaxies), with the aim of looking for similarities and systematic differences between the different sub-classes, which could provide some clues about the nature of the…
Clouds and circulation on Neptune: Implications of 1991 HST observations.
Limaye, Sanjay S.; Sromovsky, Lawrence A.; Fry, Patrick M.
Images of Neptune recorded by the Hubble Space Telescope (HST) Wide Fields/Planetary Camera in late 1991 provide a basis for the first significant comparison with the circulation results obtained from Voyager 2 observations 2 years earlier. The HST images using red (F675W) and methane band (F889N) filters contain isolated bright cloud features sui…
Cataclysmic and Close Binaries in Star Clusters. II. Probing the Core of NGC 6752 with Hubble Space Telescope
Drissen, Laurent; Paresce, F.; Shara, Michael M. +1 more
The cores of globular clusters have been predicted to be rich in close, interacting binaries. We have used the Hubble Space Telescope (HST) to test this prediction by monitoring 730 stars in the core of NGC 5752 for rapid variability. Thirty-one Faint Object Camera (FOC) images at 2200 A, with time resolution of 11 minutes, and spanning 7 hr have …
An Ultraviolet and Optical Study of Accreting Pre-Main-Sequence Stars: Uxors
Herbst, William; Eaton, Nancy L.
UX Ori stars (UXors) are pre-main-sequence stars of both the Herbig Ae/Be and T Tauri type which show aperiodic eclipse-like minima. Their variations have been attributed to occultations by circumstellar material. We use archival IUE spectra and a catalog of UBVRI photometry to study the variations of five such objects, namely, RY Lup, RY Tau, CO …